Various prior art proposals have been made to modify toilet flush tanks to a dual flush system which can be actuated at the option of the user to produce either a full flush or a partial flush. Prior U.S. Pat. Nos. 2,532,977; 2,775,772; 2,825,908; 3,141,177; 3,026,536; 3,538,519; 3,561,014; 3,561,016; 3,787,902; 3,839,746 and 4,038,708 are examples thereof.
These prior art proposals are not entirely satisfactory because of the complexity of the apparatus or the awkwardness of the control handle manipulations which are required to make them function. These difficulties have inhibited the adoption and use of the prior art proposals. In some prior art proposals, such as in McCombs U.S. Pat. No. 3,787,902 and Kertell U.S. Pat. No. 3,141,177, the flush handle must be moved in different directions to produce a full or a partial flush. In other prior art proposals, such as White U.S. Pat. No. 2,532,977 and Weisz U.S. Pat. No. 3,538,519, there are two flush handles, one for a full flush and one for a partial flush. In other prior art proposals, such as Clarke U.S. Pat. No. 2,775,772; Tucker U.S. Pat. No. 2,825,908; Johnson U.S. Pat. No. 3,561,014; Reynolds U.S. Pat. No. 3,561,016; Kowalski U.S. Pat. No. 3,839,746 and Perrine U.S. Pat. No. 4,038,708 normal actuation of a single flush handle in which it is momentarily depressed and released produces a partial flush. An abnormal manipulation of the handle, such as holding it down for a time period is required to produce a full flush. Accordingly, those unfamiliar with the mechanism will typically manipulate the flush handle for a partial flush when they really want a full flush. In other prior art proposals, such as Kertell U.S. Pat. No. 3,141,177, the flush ball actuating apparatus has to be replaced by a new apparatus specifically designed to function with the dual flush system. The patent to Wood U.S. Pat. No. 3,026,536 does produce a full flush when using the mechanism in the normal manner in which the flush handle is depressed momentarily and released, but a second actuation of the flush handle is involved in producing a partial flush.